Characteristics Of Reservoir Sedimentology Of Paleogene In Huizhou Depression, Zhujiangkou Basin

According to the theory of sedimentology, the characteristics of reservoir sedimentology of Paleogene in Huizhou depression, Zhujiangkou basin has been investigated based on core description, sample analyses and section structure. The characteristics of lithology, diageneses, sedimentary system, reservoir and influence factors of reservoir are analysed in this thesis and some main results are gotten as follow:1. By analyses of sedimentary structure, section structure and log data, sedimentary facies have been identified, two sedimentary systems have been established: river- lake-lacustrine delta of Enping Fomation and marine delta-coast of Zhuhai Fomation and their microfacies characteristics have been studied respectively. Channel bar of braided river, point bar of meandering river, subaqueous distributary channel of delta and sand flat of barrier coast compose main sandbodies of deep reservoir of paleogene in Huizhou depression.2. Taking thin sections analyses as basis, by X-ray, electronic probe, vitrinite reflectance(Ro), organic acid and other analyses, the lithology, diageneses and diagenetic evolution in study area have been studied in detail. The author concludes that compaction, cementation, replacement and formation of authigenic minerals are destructive for reservoir but early cemention is helpful to remaining primary intergranular pore and dissolution and cataclasis are both constructive diageneses, especially dissolution is a critical factor for secondary pore development, which can improve porosity and permeability greatly. The diagenetic evolution of paleogene can be divided into three stages: early diagenesis stage (A and B), middle diagenesis stage (A and B) and late diagenesis stage. Three diagenetic facies are generalized: compaction-cementation diagenetic facies, cementation-dissolution diagenetic facies and compaction diagenetic facies.3. According to the analyses of pore structure, porosity and permeability in study area, the author considers that the reservoir space of the sandbodies are dominated by intergranular dissolution pores and intragranular dissolved pores, with some primary intergranular pores, moldic pores and little intercrystalline micropores. Most of the throats are fine. Middle-fine pore with micro-fine throat is main pore-throat type. The reservoir of Paleogene in Huizhou depression is charactered by low porosity and permeability, and the reservoir quality of Zhuhai Formation is superior to that of Enping Formation.4. Based on diagenetic parameters and indexes, the author defines the reservoir of Enping Formation has a heavier diagenesis intensity than Zhuhai Formation. Most of sandstones have already entered middle diagenesis stage B, when organic acid concentration is highest, fluid-rock interaction is obvious, dissolution is intense and the evolution of I/S is showing dehydrating and expelling hydrocarbon. The secondary pore zone is main in 3500m～4000m, part devolops below 4000m where the sandstone has entered late diagenesis stage, because of cemention and filling in late diagenesis stage the secondary porosity below 4000m is lower.